This invention relates to materials and process for recording information onto a copy sheet. More specifically, the invention relates to transparent colored ferromagnetic materials for use in magnetic imaging systems.
Various systems are well known for high volume duplicating of copies including mimeograph, spirit duplicating, lithography, and the like. At the same time, there are known reproduction systems generally regarded as more suitable for lower volume rates such as xerography and photography which offer the distinct advantage of an optical input in reproducing a copy of an original.
In accordance with this invention, there is at least partially employed the process of xerography as, for example, disclosed in Carlson, U.S. Pat. No. 2,297,691, issued Oct. 6, 1942, or may include variations thereof for placing a developable image charge pattern on a support as disclosed, for example, in U.S. Pat. Nos. 2,825,814; 2,919,967; and 3,015,304. Likewise a latent magnetic image could be formed and utilized as disclosed in U.S. Pat. No. 2,857,290. As first taught by Carlson, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate area in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrostatically charged, finely-divided material such as an electroscopic powder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Hereafter, the developed xerographic image may be affixed directly to the surface on which it is developed, or as usually performed, is transferred to a secondary support on which it is affixed by any suitable means.
Now in accordance with the instant invention, there is provided selectively colored magnetic materials for use in color magnetic imaging systems.
It is, therefore, an object of this invention to provide novel materials for copy duplicating.
It is a further object of this invention to provide novel transparent ferromagnetic materials.
It is a further object of this invention to provide the formation of transparent amber to red colored materials which are magnetic.
It is a further object of this invention to provide a fine dispersion of ferrimagnetic material throughout a highly porous silicaceous material.
It is still a further object of this invention to provide a process of producing transparent magnetic particles.
It is still another object of this invention to provide transparent magnetic particles of a desired color.
The above objects and others are accomplished in accordance with this invention, generally speaking, by encasing particles of a silicaceous material in a sheath of a magnetic or magnetically-attractable material, and then heating the coated material in air to a temperature of from between about 50.degree. C. and 700.degree. C. for between about 2 minutes and about 120 minutes. The particles thus obtained are colored and are translucent to transparent which when placed near a bar magnet are attracted to the bar magnet. It is generally accepted that bodies exhibiting gross magnetic behavior must be non-transparent or opaque and are usually very dark in color. Thus, it is unusual and unexpected to discover that transparency, color, and magnetism can reside in the same body. In accordance with this invention, it has been found that after heating in the foregoing manner, the particles remain spherical and singular, but become translucent to clear in appearance and colored amber to orange to red by transmitted light, having a slight metallic luster by reflected light, and have magnetic properties. Moreover, the magnetic property is continuous in that fragments from crushed or broken bodies retain the properties of the parent body. Further, where additional color variation is desired, metal oxides and other conventional glass coloring additives may be employed to color the magnetic silicaceous bodies to any desired color to provide transparent, selectively-colored magnetic materials for use such as in magnetic color imaging systems. Obviously, other methods of modifying the color of the magnetic silicaceous materials of this invention are available such as by atmosphere control and chemically pre-treating the silicaceous particles. Such modifications are considered to be within the scope of this invention.
Generally speaking, the transparent colored magnetic materials of this invention are prepared by the solution phase thermal decomposition of transition metal carbonyls and deposition thereof onto particles of a silicaceous material followed by heating at elevated temperature in the ambient atmosphere. More particularly, the transparent colored magnetic materials of this invention are prepared by placing particles of a silicaceous material in a suitable container along with a transition metal carbonyl and a suspending medium, displacing air and moisture from the container with a dry inert gas, heating the mixture with agitation to thermally decompose the transition metal carbonyl, refluxing the mixture for up to about 24 hours at the temperature of the suspending medium whereupon the silicaceous material is coated with the elemental metal of the transition metal carbonyl, cooling the mixture, washing the metal coated silicaceous particles with fresh suspending medium, air drying the metal coated silicaceous particles, heating the metal coated silicaceous particles in a suitable container, e.g. ceramic, in air to a temperature of from between about 50.degree. C. and about 700.degree. C. for between about 2 and about 120 minutes, and cooling the metal coated silicaceous particles to room temperature in an ambient atmosphere.
Magnetically, these composite structures respond like a collection of solid, fine iron particles, but surprisingly they are translucent to transparent in the wavelength region of from about 5,000 A and above as depicted in FIG. 1. In FIG. 1, the visible absorption spectrum of the composite structures is illustrated. The spectrum was obtained on a Cary 118 spectrophotometer using a tungsten lamp source in the wavelength region of 4,000 to 8,000 Angstroms. A 0.1 mm path length quartz cell was used with the material suspended in water. The spectrum clearly indicates the transparency of the material in the region from about 5,000 to 8,000 Angstroms where absorption is at a minimum. The spectrum is that of the dispersion of .gamma.-Fe.sub.2 O.sub.3. Magnetic measurements have indicated that the composites are magnetic equivalents to their magnetic constituent, taking into account the difference in density between the composite and that of its constituent. When employing iron pentacarbonyl as the transition metal carbonyl, characterization of the magnetic silicaceous composites reveals a fine dispersion of ferrimagnetic .gamma.-Fe.sub.2 O.sub.3 (maghemite) throughout a highly porous glass matrix.
Generally, the thermal decomposition of typical transition metal carbonyls may be exemplified by the following equations for (1) iron pentacarbonyl, and (2) dicobalt octacarbonyl; ##EQU1## The decomposition of the transition metals is performed in the presence of silicaceous substrates and utilized to prepare composite materials having both chemical and mechanical stability and which display gross magnetic behavior. Substrate configuration is retained throughout the coating process. The bulk magnetic response of the composite materials may be controlled by varying the mass of the magnetic metal in proportion to the coated particle mass.
Any suitable magnetic or magnetically-attractable transition metal may be employed to coat or impregnate the substrates of the transparent colored magnetic materials of this invention. Typical such transition metals may be provided from iron pentacarbonyl, di-iron nonacarbonyl, tri-iron dodecacarbonyl, iron carbonyl cluster compounds, dicobalt octacarbonyl, nickel tetracarbonyl, other thermally extrudable compounds of such transition metals, and mixtures thereof that will not substantially hinder the optical transmission properties of the composite.
The temperature employed to produce the transparent magnetic materials of this invention depends upon the thermal properties of the composite being treated. In general, if a higher temperature is used the duration of the heat-treatment of a given composite would be shortened and vice versa. In any event, the composite exposed to the heat-treatment must be raised and maintained at a temperature sufficient to produce the desired optical and magnetic properties.
Any suitable silicaceous material may be employed as the substrate for the transparent colored magnetic material of this invention. Typical silicaceous materials include glass particles in various forms such as hollow glass beads, foam glass nodules, solid glass beads, microporous glass beads, glass chips, and fumed silica particles. In addition, vitreous materials may also be used. Thus, a wide variety of particulate materials the surface and pores of which can be coated or impregnated with a magnetic or magnetically-attractable transition metal may be employed in accordance with this invention. As indicated, the transparent colored magnetic composition of this invention may vary in size and shape. However, it is preferred that the composite material have a spherical shape as to avoid rough edges or protrusions which have a tendency to abrade more easily. Particularly useful results are obtained when the composite material has an average particle size from about 10 microns to about 300 microns, although satisfactory results may be obtained when the composite material has an average particle size of from between about 10 microns and about 850 microns. The size of the particles employed will, of course, depend upon several factors, such as the type of images ultimately developed, the machine configuration, and so forth.
The silicaceous material employed as the substrate for the composite magnetic transparent particles of this invention may have any suitable bulk density. Typically, the silicaceous material has an average bulk density of between about 0.2 and about 3.0 g/cm.sup.3. The silicaceous material employed as the substrate for the transparent magnetic composite particles of this invention may have a smooth surface, it may have cracks or fissures in the surface, and it may be porous. For example, the silicaceous material may be microporous, microreticulated silicaceous beads having an average pore size of from between about 10 A and about 500 A. The silicaceous material may have a surface area of up to about 400 m.sup.2 /gram. When the silicaceous substrate is microporous with open pores, the magnetic metal may be deposited within the carrier beads in the form of continuous threads or films which provides a practical advantage in that the magnetic metal is well protected against abrasion. It does not matter for magnetic purposes whether the magnetic material resides on the surface or is impregnated in the interior of the beads as to their performance as magnetic particles. A range of volume ratios of silicaceous material to magnetic elemental metal that will provide satisfactory magnetically responsive composite particles is from between about 5:1 to 20:1.
Any suitable solvent or suspending medium may be employed in the thermal decomposition process of preparing the low density magnetic transparent composite particles of this invention. Typical solvents and suspending mediums may be hydrocarbon solvents with boiling points preferably above that of the transition metal compound employed. Satisfactory results have been obtained with n-octane.
The transparent colored magnetic materials of the instant invention may be employed to form magnetic images on any suitable image-bearing surface including conventional photoconductive surfaces. Typical inorganic photoconductor materials include: sulfur, selenium, zinc sulfide, zinc oxide, zinc cadmium sulfide, zinc magnesium oxide, cadmium selenide, zinc silicate, calcium strontium sulfide, cadmium sulfide, mercuric iodide, mercuric oxide, mercuric sulfide, indium tri-sulfide, gallium selenide arsenic disulfide, arsenic trisulfide, arsenic triselenide, antimony trisulfide, cadmium sulfoselenide, and mixtures thereof. Typical organic photoconductors include: quinacridone pigments, phthalocyanine pigments, triphenylamine, 2,4-bis(4,4'-diethylaminophenol)-1,3,4-oxadiazol, N-isopropylcarbazole, triphenylpyrrole, 4,5-diphenylimidazolidinone, 4,5-diphenylimidazolidinethione, 4,5-bis-(4'amino-phenyl)-imidazolidinone, 1,4-dicyanonaphthalene, 1,4-dicyanonaphthalene, aminophthalocinitrile, nitrophthalodinitrile, 12,3,5,6-tetra-azacyclooctatetraene-(2,4,6,8), 2-mercaptobenzothiazole-2-phenyl-4-diphenylidene-oxazolone, 6-hydroxy-2,3-di(p-methoxyphenyl)-benzofurane, 4-dimethylaminobenzylidene-benzhydrazide, 3-benzylidene-aminocarbazole, polyvinyl carbazole, (2-nitrobenzylidene)-p-bromoaniline, 2,4-diphenyl-quinazoline, 1,2,4-triazine, 1,3-diphenyl-3-methyl-pyrazoline, 2-(4'-dimethylamino phenyl)-benzoxazole, 3-amine-carbazole, and mixtures thereof. Representative patents in which photoconductive materials are disclosed include U.S. Pat. No. 2,803,542 to Ullrich, U.S. Pat. No. 3,121,007 to Middleton, and U.S. Pat. No. 3,151,982 to Corrsin.
The magnetic transparent materials produced by the process of this invention provide numerous advantages. For example, they may be employed as pigments in such applications as in magnetic color imaging systems. Further, specifically colored low density magnetic bodies may be obtained in accordance with this invention for numerous particular applications where transparency, color, and magnetism are desired in the same body.